17,701 research outputs found
Improved quark mass density- dependent model with quark and non-linear scalar field coupling
The improved quark mass density- dependent model which includes the coupling
between the quarks and a non-linear scalar field is presented. Numerical
analysis of solutions of the model is performed over a wide range of
parameters. The wave functions of ground state and the lowest one-particle
excited states with even and odd parity are given. The root-mean squared
radius, the magnetic moment and the ratio between the axial-vector and the
vector beta-decay coupling constants of the nucleon are calculated. We found
that the present model is successful to describe the properties of nucleon.Comment: 7pages, 6 figure
Periodic Bounce for Nucleation Rate at Finite Temperature in Minisuperspace Models
The periodic bounce configurations responsible for quantum tunneling are
obtained explicitly and are extended to the finite energy case for
minisuperspace models of the Universe. As a common feature of the tunneling
models at finite energy considered here we observe that the period of the
bounce increases with energy monotonically. The periodic bounces do not have
bifurcations and make no contribution to the nucleation rate except the one
with zero energy. The sharp first order phase transition from quantum tunneling
to thermal activation is verified with the general criterions.Comment: 17 pages, 5 postscript figures include
Glueball Matrix Elements on Anisotropic Lattices
The glueball-to-vacuum matrix elements of local gluonic operators in scalar,
tensor, and pseudoscalar channels are investigated numerically on several
anisotropic lattices with the spatial lattice spacing in the range 0.1fm --
0.2fm. These matrix elements are needed to predict the glueball branching
ratios in radiative decays which will help to identify the glueball
states in experiments. Two types of improved local gluonic operators are
constructed for a self-consistent check, and the finite volume effects are also
studied. The lattice spacing dependence of our results is very small and the
continuum limits are reliably extrapolated.Comment: 3 pages, 3 figures, Lattice2003 (spectrum
A condition for first order phase transitions in quantum mechanical tunneling models
A criterion is derived for the determination of parameter domains of first
order phase transitions in quantum mechanical tunneling models. The criterion
is tested by application to various models, in particular to some which have
been used recently to explore spin tunneling in macroscopic particles. In each
case agreement is found with previously heuristically determined domains.Comment: 13 pages, 5 figure
Quantum-Classical Phase Transition of Escape rate in Biaxial Spin Particles
The escape rates of the biaxial single domain spin particles with and without
an applied magnetic field are investigated. Using the strict potential field
description of spin systems developed by Ulyanov and Zaslavskii we obtain new
effective Hamiltonians which are considered to be in exact spin-coordinate
correspondence unlike the well studied effective Hamiltonians with the
approximate correspondence. The sharp first-order transition is found in both
cases. The phase diagram of the transitions depending on the anisotropy
constant and the external field is also given.Comment: 15 pages, 8 figure
Massless Dirac Fermions, Gauge Fields, and Underdoped Cuprates
We study 2+1 dimensional massless Dirac fermions and bosons coupled to a U(1)
gauge field as a model for underdoped cuprates. We find that the uniform
susceptibility and the specific heat coefficient are logarithmically enhanced
(compared to linear-in-T behavior) due to the fluctuation of transverse gauge
field which is the only massless mode at finite boson density. We analyze
existing data, and find good agreement in the spin gap phase. Within our
picture, the drop of the susceptibility below the superconducting T_c arises
from the suppression of gauge fluctuations.Comment: 4 pages, REVTEX, 1 eps figur
Systematic Study on Fluorine-doping Dependence of Superconducting and Normal State Properties in LaFePO1-xFx
We have investigated the fluorine-doping dependence of lattice constants,
transports and specific heat for polycrystalline LaFePO1-xFx. F doping slightly
and monotonically decreases the in-plane lattice parameter. In the normal
state, electrical resistivity at low temperature is proportional to the square
of temperature and the electronic specific heat coefficient has large value,
indicating the existence of moderate electron-electron correlation in this
system. Hall coefficient has large magnitude, and shows large temperature
dependence, indicating the low carrier density and multiple carriers in this
system. Temperature dependence of the upper critical field suggests that the
system is a two gap superconductor. The F-doping dependence of these properties
in this system are very weak, while in the FeAs system (LaFeAsO), the F doping
induces the large changes in electronic properties. This difference is probably
due to the different F-doping dependence of the lattice in these two systems.
It has been revealed that a pure effect of electron doping on electronic
properties is very weak in this Fe pnictide compound.Comment: 8 pages, 5 figures, accepted for publication in J. Phys. Soc. Jp
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